Mass production surface treatment of automobile bodies has involved spray application of treatment fluids or dipping of the body into a treatment solution. Treatment baths may have various purposes including cleaning, rinsing, coating, painting, or other treatment. In the dipping process, it is customary for a conveyor to transport the object directly into the bath, entirely submerging it.
A problem with the usual dipping process is non-uniform surface treatment due to the mechanics of the dipping procedure or to entrapped air bubbles that may result in unequal processing of the surface to be treated. Also, liquid from the bath may be trapped in the body because it is not allowed to drain completely or adequately after the dipping process. This can also cause contamination of subsequent stages including electrocoating baths.